It’s been widely reported that loosely regulated gun sales in the US have fueled Mexico’s drug wars. A 2013 study by scholars at the University of San Diego’s Trans-Border Institute and the Igarape Institute — a Brazilian research center — found that 253,000 guns are smuggled into Mexico from the US each year, about 2.2 percent of total American gun sales.

Over the weekend, Alec McGillis reported for The New Republic that a similar dynamic is throwing fuel on the fire in El Salvador, Guatemala and Honduras — the three countries that account for a spike in unaccompanied refugee children showing up at our Southern border.

The surge of migrants coming to the U.S. from Central America is being fueled in part by the movement of guns heading in the other direction, from U.S. dealerships doing brisk business with the help of porous guns laws and a powerful gun lobby.

The role of gun trafficking has been oddly absent in the debate over the gang violence in Honduras, El Salvador, and Guatemala that, coupled with economic despair, is driving the migrant wave from those three nations, the so-called Northern Triangle. It’s not as if we’re unwilling to consider any U.S. responsibility for the surge—there’s plenty of talk about the fact that several of the gangs terrorizing the Northern Triangle got their start in Los Angeles, and about the role that U.S. drug policy has played in fueling violence south of the border.

Getting less attention, though, has been the U.S. link to the actual weaponry being used in the killings and other crimes that make the three Central American nations among the most dangerous in the world. (Honduras has by far the highest homicide rate in the world; El Salvador and Guatemala are fourth and fifth.) According to data collected by the ATF, nearly half of the guns seized from criminals in El Salvador and submitted for tracing in the ATF’s online system last year originated in the U.S., versus 38 and 24 percent in Honduras and Guatemala, respectively. Many of those guns were imported through legal channels, either to government or law enforcement agencies in the three countries or to firearms dealers there. But a not-insignificant number of the U.S.-sourced guns—more than 20 percent in both Guatemala and Honduras—were traced to retail sales in the U.S. That is, they were sold by U.S. gun dealers and then transported south, typically hidden in vehicles headed across Mexico, though sometimes also stowed in checked airline luggage, air cargo, or even boat shipments. (Similar ratios were found in traces the ATF conducted in 2009 of 6,000 seized guns stored in a Guatemalan military bunker—40 percent of the guns came from the United States, and slightly less than half of those were found to have been legally imported, leaving hundreds that were apparently trafficked.) “It is a problem,” says Jose Miguel Cruz, an expert in Central American gang violence at Florida International University. “The problem is we don’t have any idea how many [of the trafficked guns] there are. It’s a big, dark area.”